Panel structure for car body hood

ABSTRACT

A hood structure comprises an outer and an inner which form a closed cross section through spaces. The inner&#39;s cross-sectional shape is a sine curve, an nth-power-raised sine curve, or a spline curve having a corrugation length approximate to an outside head diameter. This corrugated hood structure can provide a uniform, excellent head impact resistance independently of impact positions on the hood. The corrugated hood structure also excels in tension rigidity, bending rigidity, and torsional rigidity. Accordingly, the car body hood panel structure satisfies requirements of head impact resistances for pedestrian protection and rigidity improvement such as the tension rigidity.

TECHNICAL FIELD

The present invention relates to a car body hood panel structure thatexcels in the head impact resistance for protecting a pedestrian and ismade of a metal material such as aluminum alloy, steel excellent in thebending rigidity, the torsional rigidity, and the like.

BACKGROUND ART

Conventionally, the panel structure of car body members such as forautomobiles uses a closed sectional structure through spaces incombination with an outer panel (hereafter simply referred to as anouter) and an inner panel (hereafter simply referred to as an inner).

The panel structures for a car hood, a roof, doors, and the likeespecially use mechanical, soldering, and adhesive means such as resinsto combine the outer and the inner that is provided at one side of theouter toward the bottom of the car body to reinforce the outer.

The inner or both the inner and the outer for these car body panelstructures are becoming using highly rigid and moldable aluminum alloyplates such as AA or JIS standard compliant 3000, 5000, 6000, and 7000series for weight saving in addition to or instead of the conventionallyused steel. Hereafter, aluminum is simply represented as Al.

Recently, car panel structures including the Al alloy plates need to behighly rigid as well as thin and light-weight. The membercharacteristics need to excel in the bending rigidity, the torsionalrigidity, and tension rigidity (dent resistance).

Conventionally, car body hood inners are available in the beam type andthe cone type. The beam-type inner provides each panel with a trimsection for weight saving. The cone-type inner has no trim section onthe basis of the closed sectional structure. Relatively large convexsections (protrusions) called cones are arranged on the cone-type innerat a regular interval. Each cone has a trapezoidal sectional view. Withrespect to the tension rigidity and the bending rigidity, a hoodstructure using this inner (cone-type hood structure) is equivalent to astructure using the beam-type inner (beam-type hood structure) inaccordance with the rigidity design of the hood. On the other hand, withrespect to the torsional rigidity, the cone-type hood structure isapproximately twice as rigid as the beam-type hood structure. Recently,special attention is paid to the cone-type hood structure.

Recently, from the viewpoint of protecting pedestrians, hood designrequirements tend to consider the safety against impact to apedestrian's head. Concerning the beam-type hood structure, there areseveral disclosures (JP-A Nos. 165120/1995, 285466/95, and 139338/93).In addition, the EEVC (European Enhanced VeHICle-Safety Committee)specifies an HIC value of 1000 or less as a hood condition with respectto the impact resistance to adult and child heads (described in EEVCWorking Group 17 Report, Improved test Methods to evaluate pedestrianprotection afforded by passenger cars, December 1998).

However, the prior art is accompanied by the following problems.

(1) [Problem 1] Increasing the Tension Rigidity

There may occur cases where the conventional cone-type and beam-typeinners cannot satisfy the demand for increased rigidity when they arethinned and made to be lightweight.

FIG. 13( a) is a longitudinal sectional view of an inner. FIG. 13( b) isa plan view of the inner. As shown in these figures, there are arrangedmany conic convex sections (protrusions) 14 at a regular interval on thesurface of a cone-type inner 13. There is formed a flat section or aconcave section 16 between the convex sections 14. The reference numeral21 represents a horseshoe bead provided at an outside periphery of thepanel. The bead 21 is universally used for reinforcing the rigidity ofthe inner As shown in FIG. 13( a), the cone-type inner 13 is joined toan Al alloy outer 12 having a specified curvature to constitute theclosed sectional structure through spaces and to be integrated into apanel structure 11. In the example of FIG. 13( a), there is provided aresin layer 15 on a flat top 14 a of the convex 14 on the inner 13. Theresin layer 15 is used to join the convex 14 of the inner 13 to a rearsurface 12 a of the outer 12. The panel periphery is hemmed (bent) to beintegrated into the panel structure.

FIG. 14 is a perspective view showing an example of applying thebeam-type inner to a car body hood. As shown in FIG. 14, the beam-typeinner 17 comprises beams 19 appropriately crossing longitudinally,transversely, and slantwise with reference to a plane direction of thepanel. The beam-type inner has a trim structure having a trimmed spacesection 20 between the beams 19. The beam-type inner 17 is also joinedto the rear surface of an outer 18 to constitute the closed sectionalstructure through spaces and to be integrated into a panel structure.

The panel structure is locally reinforced by reinforcing members such asa hinge reinforcement 21 and a latch reinforcement 22 including thecone-type inner.

These cone-type hood structures are approximately twice as rigid asconventionally used general-purpose beam-type hood structures and can beassumed to be excellent in the rigid design. This is because the closedsectional structure of the cone-type hood structure excels in therigidity against a torsional load. In addition, the cone-type hoodstructure has the bending rigidity equivalent to that of the beam-typehood structure. The cone-type hood structure does not necessarilyprovide the sufficient tension rigidity. The cone-type hood structure isrequested to increase the tension rigidity.

As a result, a relatively large, thick plate must be used for the panelat the sacrifice of weight saving in order to increase the tensionrigidity for the conventional cone-type inner.

Therefore, it is an object of the present invention is to provide a carbody hood panel structure capable of satisfying a demand for increasedrigidities such as the tension rigidity in order to take advantage ofweight saving by thinning the panel on the assumption of high torsionalrigidity characteristic of the conventional closed sectional structure.

(2) [Problem 2] Improving the Head Impact Resistance for ProtectingPedestrians

Generally, the head impact resistance evaluated in accordance with thefollowing HIC (Head Injury Criteria) value with respect to AutomobileTechnical Handbook, Vol. 3, Test and Evaluation, 2d ed. (Society ofAutomotive Engineers of Japan, Inc., Jun. 15, 1992).

HIC = [1/(t2 − t1)∫_(t1)^(t2)a 𝕕t]^(2.5)(t2 − t1)

where a is 3-axis composed acceleration (in units of G) at the headcentroid, and t1 and t2 are times having the relationship of 0<t1<t2 tocause a maximum HIC value. An operation time (t2−t1) is specified to be15 msec or less.

EEVC Working Group 17 Report specifies an HIC value of 1000 or smallerfor each of impact resistances to adult and child heads as a conditionattributed to the hood. In this report, the head impact test uses a headimpact speed of 40 km/hr. The test specifies a weight of 4.8 kg, anexternal diameter of 165 mm, and an impact angle of 65 degrees for theadult head; and a weight of 2.5 kg, an external diameter of 130 mm, andan impact angle of 50 degrees for the child head.

During the head impact test, the pedestrian's head first impacts on theouter. Then, the deformation progresses to transmit a reactive force torigid parts such as an engine in the engine room via the inner, causingan excess impact on the head. The head is subject to a firstacceleration wave and a second acceleration wave. The first accelerationwave is mainly generated by impact against the outer approximatelywithin 5 msec from the beginning of the impact. When the inner impactson a rigid object, the second acceleration wave is generatedapproximately 5 msec or later from the beginning of the impact. Theelastic rigidity of the outer mainly determines the magnitude of thefirst acceleration wave. The elastoplastic rigidity of the inner mainlydetermines the magnitude of the second acceleration wave. Deformationenergies for the outer and the inner absorb the kinetic energy at thehead. If the head's movement distance exceeds a clearance between theouter and a rigid object such as the engine, the head is directlysubject to a reactive force from the rigid object. Consequently, thehead is subject to a fatal damage equivalent to an excess impact greatlyexceeding the maximum HIC value of 1000.

(3) [Problem 2-1] Capable of Decreasing the HIC Value Despite a SmallHead Movement Distance

According as a clearance is increased between the outer and a rigidobject such as the engine, the head's movement distance can beincreased. This is advantageous to reducing the HIC value. However, thehood design inevitably is accompanied by limitations. There is a needfor a hood structure capable of reducing the HIC value despite a smallclearance and a short head movement distance.

More severe impact conditions are required especially for the adult'shead impact than for the child's head impact. An excess clearance needsto be provided between the outer and the rigid object surface beyond thedesign allowance (described in EEVC Working Group 17 Report).

As another problem, it is difficult to satisfy the HIC value of 1000 forboth children and adults with different impact characteristics along theline WAD1500 that provides a possibility of head impacts both forchildren and adults. The line WAD1500 indicates a 1500 mm distance alongthe border line from the ground surface at the car body front to thehood impact position. More particularly, the line WAD1500 for a largesedan' hood is located immediately above the engine so that just a smallclearance is left between the outer and the rigid object surface,causing a demand for effective countermeasures. (described in EEVCWorking Group 17 Report)

(4) [Problem2-2] Uniform HIC Value Independent of Impact Portions

With respect to head impact positions, a large HIC value resultsimmediately above the frame for the beam-type hood structure or at thecone vertex for the cone-type hood structure. This is because theseportions provide high local rigidity, cause small deformation ifimpacted on a rigid object, and are subject to a high reactive forcefrom the rigid object. From the viewpoint of safety, there has been ademand for a hood structure that can provide an approximately uniformHIC value independently of impact portions.

(5) [Problem 2-3] Applicability of Aluminum Material

The third problem to be solved is to provide an excellent head impactresistance despite the use of an aluminum material capable of weightsaving as a hood material. The aluminum material is often used forlight-weighting the hood. Compared to the use of the steel material,however, the use of the aluminum material is generally considered to bedisadvantageous from the viewpoint of protecting pedestrians. This ismainly because the elastic modulus and the gravity of the aluminummaterial are approximately one third of those of the steel material. Ifthe hood is used to absorb the kinetic energy of the head, the membranerigidity and the weight of the aluminum hood as the panel structure areinsufficient compared to those of the steel hood.

The bending rigidity of a plate material is proportional to ET³, where Eis a Young's modulus and T is a plate thickness. The membrane rigiditythereof is proportional to ET. When the steel material (Young's modulusEs, plate thickness Ts, and gravity γs) is replaced by the aluminummaterial (Young's modulus Ea, plate thickness Ta, and gravity γa), theplate thickness is determined as follows so that the same bendingrigidity results.EaTa³=EsTs³Ea/Es=1/3

Hence,Ta/Ts=3^(1/3)=1.44

A membrane rigidity ratio of the aluminum hood to the steel hoodbecomes:(EaTa)/EsTs=1.44/3=0.48

A weight ratio thereof becomes:(Taγa)/(Tsγs)=1.44/3=0.48

The membrane rigidity and the weight of the aluminum hood are just 0.48times as large as those of the steel hood. As a result, when the headimpacts on the hood, the head movement distance increases and the headeasily impacts on a rigid object. The outer absorbs a small energy atthe first acceleration wave, increasing the second acceleration wave.Accordingly, the conventional hood structure increases the HIC value,making it very difficult to satisfy limits of the HIC value.

Of course, making Ta equal to a triple of Ts provides the same membranerigidity ratio and weight ratio as those for the steel hood. However,this causes excess costs, unpractical for the design.

In this manner, it is very difficult to use the aluminum material forthe hood and limiting conditions for the head impact under thiscondition. Of course, if there is found an aluminum hood structure thatsatisfies this condition, a steel hood employing this structure canfurther decrease the HIC value.

As mentioned above, the following summarizes problems to be solved forthe hood structure from the viewpoint of pedestrian protection asanother object of the present invention.

(a) Capable of decreasing the HIC value despite a small head movementdistance;

(b) Providing the approximately uniform HIC value independently ofimpact portions on the hood; and

(c) Capable of sufficiently decreasing the HIC value even using analuminum hood.

DISCLOSURE OF THE INVENTION

In order to achieve these objects, the car body hood panel structureaccording to the present invention is expressed as a closed sectionalstructure comprising a combination of an outer panel and an inner panelthrough spaces, wherein a plurality of corrugated beads is providedparallel to each other on an entire surface of the inner panel and across-sectional shape of the inner panel is corrugated.

There is provided the inner having a corrugated cross section (hereafterreferred to as the corrugated inner) as mentioned above. If the car bodyhood panel structure using the corrugated inner (hereafter referred toas the corrugated hood structure) comprises the outer and the innerwhich are thinned, it is possible to drastically improve the tensionrigidity of the hood structure. In addition, the bending rigidity andthe torsional rigidity can be also ensured sufficiently. As a result,the hood can be suppressed from being deformed against external loads.

Further, with respect to pedestrian protection, it is possible toimprove the resistance to impact between the head and the hood forhigher safety. Consequently, the following features can be provided.

(a) Capable of decreasing the HIC value despite a small head movementdistance;

(b) Providing the approximately uniform HIC value independently ofimpact portions on the hood; and

(c) Capable of sufficiently decreasing the HIC value even using analuminum hood.

In addition, the panel structure according to the present inventionfeatures a simple configuration using the above-mentioned corrugatedinner. It is possible to increase the tension rigidity and the bendingrigidity, and enable weight saving without increasing the inner platethickness as conventionally practiced. A flat panel can be easilypress-molded into the above-mentioned corrugated inner, makingmanufacture of the inner itself easy.

Moreover, as mentioned above, the panel structure according to thepresent invention is capable of improving the rigidity as the panelstructure itself. It is possible to use a light aluminum alloy as amaterial for the outer and the inner.

From the viewpoint of hood weight saving, the hood tension rigidity canbe improved drastically by means of the corrugated inner and thecorrugated hood structure using the same according to the presentinvention. It is possible to provide the hood structure fully featuringthe torsional rigidity and the bending rigidity. From the viewpoint ofpedestrian protection, it is possible to provide the hood structureexcellent in the head impact resistance. In this case, the hoodstructure, if made of aluminum, can sufficiently decrease HIC valueseven through a small clearance between the outer and a rigid object andcan provide approximately uniform HIC values independently of impactpositions on the hood. Furthermore, it is possible to provide thecone-type hood structure using the steel outer excellent in the headimpact resistance for pedestrian protection.

In order to achieve these effects, the above-mentioned corrugated shapepreferably traces a sine curve or an nth-power-raised sine curve. Thenth-power-raised sine curve refers to a group of curves using sin^(n)(θ), where θ indicates a parameter representing a position and nindicates an integer greater than or equal to 1. The static rigidity ofthe hood can be improved through the use of the corrugated inner whosecorrugated shape follows the sine curve or the nth-power-raised sinecurve. Furthermore, it is possible to decrease the head acceleration fora head impact from the viewpoint of pedestrian protection.

In addition, it is preferable that the plurality of corrugated beads isprovided in any arrangement selected from those which are parallel orslantwise against a longer direction of the panel structure, concentricapproximately around the center of the panel structure, and doublycorrugated as a combination of these arrangements. Since the corrugatedinner uses the plurality of corrugated beads provided in any arrangementselected from those which are parallel or slantwise against a longerdirection of the panel structure, concentric approximately around thecenter of the panel structure, and doubly corrugated as a combination ofthese arrangements, the static rigidity of the hood can be improved.Furthermore, it is possible to decrease the head acceleration for a headimpact from the viewpoint of pedestrian protection.

It is possible to formulate a preferable range of corrugation length pof the corrugated inner based on a sine wave with reference to outsidehead diameter d as follows in case of a head impact for pedestrianprotection from the viewpoint of impact resistance improvement.0.7<p/d<1.7

This range is effective for decreasing HIC values.

It is possible to formulate a preferable range of corrugation height hof the corrugated inner based on a sine wave with reference to outsidehead diameter d as follows in case of a head impact for pedestrianprotection from the viewpoint of impact resistance improvement.0.15<h/d<0.4

This range is effective for decreasing HIC values.

That is to say, HIC values greatly decrease through the use of thecorrugated inner whose corrugation height and corrugation length satisfythe preferable ranges. It is possible to provide the hood structureexcellent in the head impact resistance.

When the inner panel is locally provided with a reinforced plate, thehead impact resistance can be increased at the reinforced position. Itis possible to provide the hood structure capable of locally improvingthe head impact resistance at a position where there is a smallclearance between the outer and the rigid object surface.

When there is provided the method of softly joining the outer and theinner, tops of the corrugated inner is provided with local bondingsections in a cross-stitched or distributed manner. Since very softjoining sections are provided, there is no sacrifice of a backlashvibration between the outer and the inner during a head impact from theviewpoint of the pedestrian protection. As a result, the headacceleration waveform is disturbed to enable the HIC value to bedecreased.

The invention uses the inner (hereafter referred to as the spline-typeinner) whose corrugated shape is defined by a spline function.Consequently, the corrugated inner can be designed in consideration forarrangement of complicated rigid parts in an engine room. It is possibleto decrease HIC values and improve the head impact resistance.

The invention can efficiently absorb a head impact energy by means ofthe steel outer having large membrane rigidity and weight, control thehead's first acceleration wave to an appropriate size, and efficientlyabsorb the remaining impact energy by means of the aluminum alloycorrugated inner or the like excellent in the bending rigidity. As aresult, it is possible to provide the light-weight and economical hoodstructure excellent in the head impact resistance.

The invention can provide the light-weight and economical hood structureexcellent in the head impact resistance.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view showing an example of an inner according tothe present invention;

FIG. 2 is a sectional view taken along lines A—A of a corrugated hoodstructure using the inner in FIG. 1;

FIG. 3 is a perspective view of the corrugated hood structure in FIG. 2;

FIG. 4 is a perspective view showing another example of the corrugatedinner according to the present invention;

FIG. 5 is a perspective view showing still another example of thecorrugated inner according to the present invention;

FIG. 6 is a perspective view showing yet another example of thecorrugated inner according to the present invention;

FIG. 7 is a perspective view showing still yet another example of thecorrugated inner according to the present invention;

FIG. 8 is a perspective view showing yet still another example of thecorrugated inner according to the present invention;

FIG. 9 is a perspective view showing still yet another example of thecorrugated inner according to the present invention;

FIG. 10 is a perspective view showing finally, yet still another exampleof the corrugated inner according to the present invention;

FIG. 11 illustrates load conditions onto the hood structure, whereinFIG. 11A is a perspective view showing a bending load and FIG. 11B is aperspective view showing a torsional load;

FIG. 12 shows a schematic sectional view of the corrugated hoodstructure using a spline-type inner along a car width direction at thehood center;

FIG. 13 shows a conventional cone-type hood structure, wherein FIG. 13Ais a longitudinal sectional view of the cone-type hood structure andFIG. 13B is a plan view of the cone-type inner;

FIG. 14 is a perspective view showing a conventional beam-type hoodstructure;

FIG. 15 is an analysis model diagram of the cone-type inner in FIG. 13B;

FIG. 16 is a schematic diagram (side view) showing a head impact modelfor the corrugated inner according to the present invention;

FIG. 17 is a schematic diagram (front view) showing the head impactmodel for the corrugated inner according to the present invention;

FIG. 18 is a model diagram (perspective view) showing the corrugatedinner and the head model;

FIG. 19 is a model diagram (perspective view) showing the conventionalbeam-type inner and the head model;

FIG. 20 is a perspective view showing an example of a reinforced sectionof the corrugated inner according to the present invention;

FIG. 21 is a perspective view showing an example of a bonded partbetween the outer and the corrugated inner according to the presentinvention;

FIG. 22 is an explanatory diagram showing head acceleration waveformsfor the beam-type hood structure and the corrugated hood structure;

FIG. 23 is an explanatory diagram showing effects of corrugation lengthsfor the corrugated hood structure according to the present invention onHIC values;

FIG. 24 is an explanatory diagram showing effects of corrugation heightsfor the corrugated hood structure according to the present invention onHIC values;

FIG. 25 is a perspective view of the corrugated hood structure showinghead impact positions;

FIG. 26 is an explanatory diagram showing effects of clearance L betweenthe outer and a rigid object side on HIC values through a combination ofan adult head impact, a child head impact, the corrugated hoodstructure, and the beam-type hood structure;

FIG. 27 is an explanatory diagram showing an example of the corrugatedinner provided with a corrugated bead at a hood periphery;

FIG. 28 is a perspective view showing a spline-type inner inconsideration for arrangement of a rigid object in the engine room;

FIG. 29 is an explanatory diagram of the spline-type inner showing arigid object side position in the engine room, impact positions 1through 4 along WAD1500, and impact positions 5 through 8 along WAD1100,wherein the rigid object position is provided 70 mm perpendicularlybelow the outer;

FIG. 30 shows a head acceleration waveform for the child head impact atimpact position 1;

FIG. 31 shows a head acceleration waveform for the adult head impact atimpact position 1;

FIG. 32 shows an analysis result of the child head impact;

FIG. 33 shows an analysis result of the adult head impact;

BEST MODE FOR CARRYING OUT THE INVENTION

Several preferred examples of the corrugated hood structure according tothe present invention will be described below with reference to theaccompanying drawings.

First, an example of the corrugated hood structure according to thepresent invention will be described. FIG. 1 is a perspective view of theinner. FIG. 2 is a sectional view taken along lines A—A of FIG. 1. FIG.1 is meshed for easy understanding of the corrugated form according tothe present invention.

An inner 1 a in FIGS. 1 and 2 is made of light-weight and high-tensionmetal such as an aluminum alloy and a high-tension steel plate. There isprovided a plurality of corrugated beads (convex streak) 2 aapproximately parallel along the car length direction all over the panelexcept peripheries 9 a (toward the car front), 9 b (toward the driverseat), 10 a and 10 b (along the car side). The approximate parallelrelationship is applied to not only straight corrugated beads, but alsocurved corrugated beads such as concentric circles and ovals to bedescribed later.

As shown in the sectional view of FIG. 2, a corrugated bead 2 a forms acorrugated shape comprising a continuous sine curve along the car width.The corrugated bead 2 a comprises a convex streak 5 and a concave streak6. The convex streak 5 is protruded toward the rear of the outer and hasa cross section forming a gentle arc or a rib in the longer direction.On the contrary, the concave streak 6 is depressed and likewise has across section forming a gentle arc or a rib in the longer direction. InFIGS. 1 and 2, seven straight corrugated beads 2 a are approximatelyparallel provided independently of each other (with an interval) on thesurface of the inner 1 a.

The corrugated beads 2 a in FIGS. 1 and 2, including the concave streaks6, have approximately the same width across the longer direction.However, the corrugated beads 2 a including the concave streaks 6 neednot always have the same width across the longer direction. From aplanar viewpoint, for example, it may be preferable to provide a locallynarrowing constriction or dent functioning as a starting point for theoverall deformation of the inner in case of a car collision to absorb ashock and protect fellow passengers. Alternatively, the corrugated beads2 a may be formed to be gradually narrowing or expanding in accordancewith the car body design.

The conditions for the corrugated beads 2 a and the concave streaks 6such as the sectional shape (width, height, tilt angle for the slope),the number of beads, the length, and the like are not limited to thisembodiment. In consideration for the optimization of the rigidity andthe ease of molding, it is preferable to select the corrugation height hfrom the range between 10 and 60 mm and the corrugation length p fromthe range between 90 and 300 mm.

For example, it is possible to increase the rigidity of the inner or thepanel structure according as the corrugated beads including the concavestreaks form a large cross sectional shape, many corrugated beads areprovided, and corrugated beads are provided all over the panel.

Accordingly, the sectional shape and condition of the corrugated beams 2a and the concave streaks 6 are appropriately selected in considerationfor the relationship among the tension rigidity, the torsional rigidity,and the bending rigidity requested for the rigidity design, and acriterion whether molding is possible or easy (moldability).

For further light-weighting the inner, it may be preferable to providethe corrugated bead 2 a and the concave streak 6 with a space or acutout (any shape such as a circle, a rectangle, or the like) bypartially trimming the panel so as not to affect the rigidity and thestrength.

Further, it may be preferable to appropriately combine another rigidityreinforcing means. For example, the inner may be made as a tailor blankto thicken the inner's outside periphery compared to the center platethickness and to improve the bending rigidity of the panel or the panelstructure against a bending load applied to the edge of the panel or thepanel structure.

(Cross-Sectional Shapes of the Inner)

Cross-sectional shapes of the inner according to the present inventionmay be defined by a sine-curve corrugation or an nth-power-raised sinewave. Further, it may be preferable to adjust the local rigidity byproviding small concaves and convexes on the sine curve or thenth-power-raised sine curve.

(Arranging the Corrugated Beads on the Inner)

Perspective views in FIGS. 4 through 10 show examples of arranging thecorrugated beads on the corrugated inner according to the presentinvention. Integration of the inner and the outer basically follows thesame manner or procedure as that for the panel structure described inFIG. 2. Like FIG. 1, FIGS. 4 through 10 are also meshed.

When the corrugated inner according to the present invention is observedfrom a planar viewpoint, it is preferable to arrange the corrugatedbeads parallel to each other so as to be parallel or oblique against thelonger direction of the hood, concentric or oval approximately aroundthe center of the corrugated inner, and doubly corrugated as acombination of these arrangements. The corrugated beads arranged inthese manners configure a cross-sectional shape of the inner across theoverall panel. It should be noted that these specific arrangements arenot strictly specified. The specification includes the meaning ofapproximation such as “approximately parallel” or “approximatelyconcentric” in terms of permitting allowable tolerances as far as aneffect of improving the rigidity is not impaired.

An inner 1 b in FIG. 4 is provided with a plurality of corrugated beads2 b approximately parallel to each other and concentrically all over thepanel.

An inner 1 c in FIG. 5 is provided with a plurality of corrugated bead 2c and 2 d approximately parallel to each other and ovally all over thepanel.

An inner 1 d in FIG. 6 is provided with a plurality of corrugated beads2 a and 2 e vertically and horizontally at right angles to each other toincrease an adhesion area between the outer and the inner. Likewise, aninner 1 e in FIG. 7 is provided with a plurality of corrugated beads 2 a(vertical bead) and 2 e (horizontal bead) vertically and horizontally atright angles to each other to decrease an adhesion area between theouter and the inner.

Inners 1 f and 1 g in FIGS. 8 and 9 indicate embodiments ofapproximately parallel distributing corrugated beads 2 f and 2 g in a Vor U shape.

An inner 1 h in FIG. 10 shows an embodiment of crossing the obliquecorrugated beads 2 f and 2 g in FIGS. 8 and 9 with each other.

(Hood Structure)

The following describes the hood structure as an integration of theinner and the outer.

The hood structure in FIG. 2 uses a resin layer 7 arranged on a top 5 aof a corrugated bead 5 of the inner 1 a. The resin layer works as anadhesive to join a flat top 3 a of the corrugated bead 2 a with the rearof an outer 4 a formed in a gentle arc to be integrated into a closedsectional structure through spaces.

The inner 1 a and the outer 4 are fastened together with the adhesive tobe integrated into the hood structure by hemming a hem 4 b around theouter 4.

The resin layer 7 can be provided with damping, sound-muffling(soundproof), shock-absorbing effects, and the like by selecting resincharacteristics and types. In order to improve these effects, it may bepreferable to fill the resin layer, a cushioning material, and the likenot only at the top Sa of the corrugated bead 5, but also on the concavestreak 6, i.e., into a gap between the inner 1 a and the outer 4.

FIG. 3 is a perspective view of the corrugated hood structure in FIG. 2.In FIG. 3, the inner 1 a and the outer 4 are integrated into acorrugated hood structure that can be locally reinforced by reinforcingmembers such as the hinge reinforcement 21 and the latch reinforcement22 like the conventional cone-type hood structure and beam-type hoodstructure as mentioned above.

(Mechanism for Improving the Rigidity)

The following describes the mechanism for improving the panel's localbending rigidity and improving the rigidity as the inner or thecorrugated hood structure by using the corrugated bead 2 a and bycorrugating the inner.

Firstly, the tension rigidity is a local rigidity with reference to theconcentrated load at the center of the outer. The concentrated loadperpendicularly acts on the outer surface from the outer to the inner.

Secondly, the bending rigidity is a rigidity against a bending loadapplied to the hood structure shown in FIG. 11A. Bending load Fb mainlyacts on the end of the hood in the vertical direction. The bending loadFb is a concentrated load acting on both ends D and E at the front basedon three bearing points of the hood 1, namely, ends A and B at thedriver seat side and the center C of the front. Bending rigidity Kb is avalue defined as a ratio of the bending load Fb to displacement Ub(Kb=Fb/Ub) at loading points D and E.

And thirdly, the torsional rigidity is a rigidity against a torsionalload applied to the hood structure in FIG. 11B. The torsional load,represented as Ft, mainly acts on the hood front end in the verticaldirection (from the bottom to the top). The torsional load Ft is aconcentrated load acting on one end D at the front based on threebearing points of the hood 1, namely, ends A and B at the driver seatside and one end E of the front. Torsional rigidity Kt is a valuedefined as a ratio of the torsional load Ft to displacement Ut(Kt=Ft/Ut) at the loading point D.

Of these rigidities, the tension rigidity is characterized as follows.Compared to the cone-type hood structure, the corrugated hood structureprovided with the corrugated inner increases local bending rigiditiesdue to concaves and convexes at the center of the corrugated inner. Inaddition, the bonded area between the inner and the outer increases. Theload transmission from the outer to the inner is distributed to a widerange, suppressing the displacement at loading points. As a result, thetension rigidity increases.

The bending rigidity is characterized as follows. Compared to thecone-type hood structure, the corrugated hood structure increases across sectional area effective for improving the bending rigidity due tothe corrugated shape. As a result, the hood's bending rigidityincreases.

Further, the torsional rigidity is characterized as follows. The closedsectional structure used for the cone-type hood structure and thecorrugated hood structure helps improve the torsional rigidity.Basically, the closed sectional structure provides the torsionalrigidity approximately twice as large as the conventional beam-type hoodstructure. However, concaves and convexes at the center of thecorrugated inner act to slightly decrease the torsional rigidity.Accordingly, the torsional rigidity of the corrugated hood structurebecomes equal to or slightly smaller than that of the cone-type hoodstructure. On the other hand, the closed sectional structure originallyprovides a high torsional rigidity and can sufficiently satisfy thedesign condition even if the original torsional rigidity slightlydecreases.

In this manner, the corrugated hood structure according to the presentinvention is superior to the cone-type hood structure in the tensionrigidity and the bending rigidity but is slightly inferior to thecone-type hood structure in the torsional rigidity. Since the designcondition is fully satisfied, however, the corrugated hood structureaccording to the present invention can provide the hood structure havinghigh rigidities in view of the hood design requirements.

(Mechanism to Improve the Head Impact Resistance for ProtectingPedestrians)

From the viewpoint of solving problems about an impact between the headand the hood for the purpose of protecting pedestrians, the corrugatedinner can very satisfactorily absorb the head's kinetic energy andgreatly decrease the HIC value. This is because of the following:

(a) Corrugation length p of the corrugated inner is defined to be avalue approximate to the outside head diameter. When a head impactoccurs, one corrugation approximately supports the head and generatesdeformation for gently catching the head. As a result, the secondacceleration wave reduces to decrease the HIC value.

(b) When a head impact occurs, the outer and the inner cause a backlashvibration to disturb the head acceleration waveform. As a result, it ispossible to greatly reduce the second acceleration wave to decrease theHIC value.

There may be generated a small clearance between the outer and the rigidobject surface when the head impacts immediately above the engine, forexample. In such case, it may be preferable to provide a reinforcingplate to the corresponding part of the corrugated inner to increase thelocal rigidity. This can improve the impact resistance and decrease theHIC value in exchange for a slight increase in the weight.

It may be preferable to apply the soft joint method between the outerand the inner to provide tops of the corrugated inner with local bondingsections in a cross-stitched or distributed manner. There is nosacrifice of a backlash vibration between the outer and the inner duringa head impact from the viewpoint of the pedestrian protection. As aresult, the head acceleration waveform is disturbed to enable the HICvalue to be decreased.

When the spline-type inner is applied, a more realistic design becomesavailable in consideration for the arrangement of rigid parts such as anengine, a battery, a radiator, and the like in the engine room.

The design of the corrugated inner needs to consider the arrangement ofrigid parts such as the engine, the battery, the radiator, and the likein the engine room. The arrangement of these parts largely depends oncars. The cross-sectional shape of the corrugated inner needs to bemodified from a simple, regular form into a corrugated form withirregularly varying corrugation lengths, heights, and shapes. For thisreason, the corrugated cross-sectional shape must be principallycompliant with one as shown in FIG. 12 that can be defined by formfunctions capable of representing any three-dimensional forms such as aspline function. Here, let us define the inner having such corrugatedshape according to a spline function as a spline-type inner that isassumed to be one mode of corrugated inners.

FIG. 12 shows a cross-sectional shape at a given cross section along thelonger direction of the hood including an outer, a spline-type inner,and a rigid object surface in the engine room. If a consideration ismade about the positional relationship between the spline-type inner andthe rigid object surface, they need to be configured so that bottoms ofthe corrugations approximately evenly impact on the rigid object surfaceand that a reactive force from the rigid object surface propagates tothe entire surface of the corrugated inner. At position B1, there is asmall clearance between the outer and the rigid object surface toinevitably cause an impact between the head and the rigid object. Thecross-sectional shape must be configured so that position B1 is evenlysupported at bottoms D1 and D2 of the spline corrugation. The sameapplies to positions B2, B3, and B4. By contrast, at position A1, thereis a sufficient clearance to cause no impact on the rigid object. Inthis case, the cross-sectional shape must be configured so that asufficient corrugation length is ensured and position A1 is evenlysupported at bottoms D2 and D3 of the spline corrugation. If thecorrugation length is shortened and a plurality of corrugations isprovided at this position, the inner's bending rigidity decreases alongthe car width direction. Consequently, displacements increase in thevertical direction to decrease the head impact resistance. Onecorrugation must be used to cover a distance from positions D2 to D3.The same applies to position A2. As long as the HIC value is small,there is no problem of providing allowable corrugations. With respect toa head impact at bottoms C1, C2, C3, C4, and C5 of the corrugation, aload is first transmitted to inner tops, and then is transmitted to therigid object surface via the inner bottoms. The impact resistancebecomes approximately the same as that for an impact on the tops. Inthis manner, the spline-type inner can provide the approximatelyconstant head impact resistance independently of the arrangement ofrigid objects in the engine room while such arrangement varies from onecar to another.

The arrangement of rigid objects in the engine room is very complicated.Heights and lengths of spline corrugations need to flexibly vary in thecar width direction and the longer direction of the car. Accordingly,the spline-type inner is shaped to be a complexly curved surface.

At a position that is subject to an insufficient clearance and aninsufficient head impact resistance, it is preferable to provide theinner with a reinforcing plate, locally provide the spline-type innerwith concaves and convexes (i.e., embossing finish), or overlap smallcorrugations in the longer direction of the hood. In this manner, it ispossible to enhance the inner's local rigidity and improve the headimpact resistance.

According to another feature of the invention, the corrugated hoodstructure comprising an outer panel made of steel and an inner panelmade of aluminum alloy. This hood structure can provide lightweight anda high head impact resistance. It is possible to effectively decreasethe HIC value especially for the adult head impact that requires a highhead impact resistance.

Further, the cone-type hood structure may comprise an outer panel madeof steel and an inner panel made of aluminum alloy. This hood structurecan provide lightweight and a high head impact resistance. It ispossible to effectively decrease the HIC value especially for the adulthead impact that requires a high head impact resistance.

The hood of a large sedan, for example, needs to satisfy head impactsfor both children and adults. The following clarifies that thelight-weight and economical hood is preferably structured to comprise anouter made of steel and an inner made of aluminum alloy. According to apublicly known document (Okamoto, Concept of hood design for possiblereduction in head injury, 14th ESV conference, 1994), it is known thatan ideal head acceleration waveform causes the HIC value ofapproximately 1000 if the first acceleration wave is approximately 200G. After conducting an analysis, we found that this condition isequivalent to the case where a child head impacts on the steel outer 0.7mm thick. The HIC value becomes 1000.

It is possible to say that functions needed for the outer are increasingthe first acceleration wave as much as possible, decreasing verticaldisplacements of the head as much as possible by means of the outer'sabsorption of an impact energy, and decreasing the second accelerationwave due to an impact between the inner and the rigid object surface.(It should be noted that the maximum plate thickness is approximately0.7 mm for a steel plate. Exceeding this plate thickness causes animproper effect that only the first acceleration wave for a child headimpact generates an HIC value exceeding 1000.) The weight and themembrane rigidity of the outer are necessary for improving energyabsorption by the outer. A preferable material is steel from theeconomical viewpoint. An aluminum alloy is capable of weight saving andis equivalent to the steel in terms of the bending rigidity. However,the aluminum alloy is unsuitable as an outer material because its lightweight bottlenecks adversely.

On the other hand, functions needed for the inner are absorbing anexcess energy resulting from energies consumed for an impact between thehead and the outer and decreasing the second acceleration wave due to areactive force from a rigid object surface such as the engine. If thecorrugated hood structure is deformed until the head touches the rigidobject surface, the HIC value largely exceeds 1000. When the corrugatedhood structure is assumed, a function required of the inner is to fullyabsorb the remaining energy by means of deformation of the bent innerwithin a specified clearance. In this case, a preferable material is thealuminum alloy capable of weight saving and providing a high bendingrigidity. According to these reasons, the corrugated hood structurecomprising the steel outer and the aluminum alloy inner provideslight-weight and economical hoods for large sedans and the like thatneed to satisfy head impacts for both children and adults.

(Applicable Metals)

Metals used for the panel according to the present invention areappropriately selected from generally used Al alloyplates, high-tensionsteel plates, and the like. However, the use of resin is impractical andis not applied to the panel according to the present invention. This isbecause the resin must be extremely thickened due to its characteristicssuch as the material strength in order to provide the rigidity requiredfor the present invention.

The use of an Al alloy is preferable for further weight saving of thecar body. The corrugated hood structure according to the presentinvention is fully applicable to high rigidity without usinghigh-tension steel plates or specially high-tension Al alloys.

In consideration for this, it is preferable select materials for theinner and the outer according to the present invention for car bodiesfrom relatively high-bearing general-purpose (standard) Al alloy platessuch as AA or JIS standard compliant 3000, 5000, 6000, and 7000 seriesthat are generally used for this type of panels. These Al alloy platesare manufactured by normal methods such as metal rolling and areappropriately subject to conditioning processes for use.

(Examples of Increasing Rigidities According to Problem 1)

We then conducted an FEM analysis for the panel structure according tothe present invention and compared the bending rigidity, the torsionalrigidity, and the tension rigidity of the corrugated hood structureaccording to the present invention with those of the conventionalcone-type hood structure.

Table 1 shows an analysis result. Invention examples 1 through 8correspond to examples in FIGS. 1 and 4 through 10, respectively. InTable 1, values for the bending rigidity ratio, the torsional rigidityratio, and the tension rigidity ratio are represented with reference tothe corresponding values each assumed to be 1 for the cone-type hoodstructure (comparative example 9).

The analysis model is assumed to be a normal sedan hood and comprisesonly an outer and an inner both made of Al alloy. The analysis model isa simple model configured to be a double-plate structure having doublecurvatures, i.e., a curvature of 3100 mm in a longer direction of thehood and a curvature of 4300 mm in a width direction. The outer has aplate thickness of 1.0 mm. The inner has a plate thickness of 0.8 mm.

The cross-sectional shape of the inner according to the presentinvention follows a sine curve. The corrugation length is 174 mm. Thecorrugation height is 25 mm. The cross-sectional shape of a single conein the cone-type inner has an outside bottom diameter of 140 mm and anoutside top diameter of 20 mm. The cone height is 25 mm. There areevenly arranged 33 such cones at a 170 mm interval as illustrated by aperspective view in FIG. 15.

Invention example 1 (the vertically corrugated bead in FIG. 1) showsremarkable improvement in the tension rigidity and a 10% increase in thebending rigidity. The torsional rigidity is equivalent to that of thecone-type inner. On the whole, it can be understood that the rigiditiesincrease greatly.

Like invention example 1, invention example 2 (the concentricallycorrugated bead in FIG. 4) increases the tension rigidity and thebending rigidity but decreases the torsional rigidity 5%. As mentionedabove, however, the cone-type hood structure provides the torsionalrigidity twice as large as that of the conventional beam-type hoodstructure. It can be understood that the torsional rigidity of thisinvention example fully satisfies the design conditions and that, as aresult, the rigidities increase greatly on the whole.

Invention example 3 (the ovally corrugated bead in FIG. 5) isapproximately the same as invention example 2. It can be understood thatthe rigidities increase greatly on the whole.

Invention example 4 (the vertically and horizontally double corrugatedbead in FIG. 6) increases the bonded area between the inner and theouter. Accordingly, it can be understood that the bending rigidity andthe torsional rigidity slightly decrease but the tension rigidityincreases.

Invention example 5 (the vertically and horizontally double corrugatedbead in FIG. 7) decreases the bonded area between the inner and theouter. Accordingly, it can be understood that the bending rigidity andthe tension rigidity increase.

Invention example 6 (the inverted V-shaped corrugated bead in FIG. 8)and invention example 7 (the V-shaped corrugated bead in FIG. 9)increase the bending rigidity and the tension rigidity 20%. It can beunderstood that the rigidities increase greatly on the whole.

Invention example 8 (the slantwise double corrugated bead in FIG. 10)increases the tension rigidity 10%. It can be understood that therigidities increase greatly on the whole.

According to these results, the corrugated hood structure according tothe present invention greatly increases the tension rigidity and thebending rigidity. As a result, it is possible to thin the inner or theouter for weight saving.

TABLE 1 Inner panel shape Rigidity Bead cross section of the hoodstructure Arrangement of Corrugation Corrugation Bending TorsionalTension corrugated length height rigidity rigidity rigidity Legend No.beads (mm) (mm) ratio ratio ratio In- 1 FIG. 1 (vertical) 174 25 1.1 1.01.4 vention 2 FIG. 4 (concentric) 174 25 1.1 0.95 1.2 example 3 FIG.5(oval) 174 25 1.1 1.0 1.1 4 FIG. 6 (double 174 25 0.9 0.7 1.1corrugated) 5 FIG.7 (double 174 25 1.1 0.9 1.1 corrugated) 6 FIG.8(inverted 174 25 1.2 0.95 1.2 V-shaped) 7 FIG. 9 (V-shaped) 174 25 1.20.8 1.2 8 FIG. 10 (double 174 25 1.0 0.75 1.1 corrugated) Com- 9 FIG. 13(conical) 1.0 1.0 1.0 parative Outside bottom example diameter 140 mmφOutside top diameter 20 mmφ Height 25 mm

According to these results, the corrugated hood structure according tothe present invention greatly increases the tension rigidity and thebending rigidity. As a result, the present invention can thin the inneror the outer for weight saving.

(Examples for Improving Head Impact Resistances According to Problem 2)

We built a simple analysis model concerning improvement of head impactresistances for pedestrian protection and examined effects of thecorrugated hood structure. We made the examination under the conditionsthat the corrugated cross section is a sine wave and corrugations aredistributed parallel to each other along a longer direction of the hood.

The analysis model is configured as follows. FIG. 16 is a side viewschematically showing a pedestrian's head impact model for thecorrugated inner according to the present invention. FIG. 17 is a frontview of the model. FIG. 18 is a perspective view showing the head impactmodel in FIGS. 16 and 17.

In FIGS. 16 and 17, the reference numeral 1 denotes a corrugated inner,4 an outer, 23 a pedestrian's head, 24 a rigid object surface, and 30 anadhesive such as resin. With respect to measurements, the referencesymbol d represents an outside head diameter, V an impact speed, α animpact angle, L an interval between the outer and the rigid objectsurface along an impact direction, c an adhesive thickness, h acorrugation height of the corrugated inner, and p a corrugation lengthof the corrugated inner.

FIG. 19 shows a beam-type inner model as a comparative example togetherwith a pedestrian's head model. FIG. 20 shows a model of the corrugatedinner provided with a locally reinforced plate in order to decrease theHIC value to be described later. FIG. 21 shows an example of arrangingbonding sections on the corrugated inner.

Table 2 lists analysis conditions for the pedestrian's head models inFIGS. 16, 20, and 21. Table 3 lists shapes of the pedestrian's headmodels.

TABLE 2 Item Adult Child Weight W 4.8 kg 2.5 kg Outside head diameter d165 mm 130 mm Impact angle α 65 degrees 50 degrees Impact speed v 40km/h 40 km/h Skin thickness ts 7.5 mm 7.5 mm Skin's elastic modulus Es 2kg/mm² 3 kg/mm²

TABLE 3 Beam-type Item Corrugated hood structure hood structure Headmodel Unit Child 1.27 times Adult Child Adult Outside head mm 130 165165 130 165 diameter d Corrugation mm 25 32 32 height h Corrugation mm165 210 165 length p Clearance mm 29 29 29 29 29 between outer and innerBonding section mm 4 4 4 4 4 thickness c Outer plate mm 1.0 1.27 1.0 1.01.0 thickness Inner plate mm 0.8 1.02 0.9 0.8 0.9 thickness Reinforcedplate mm 0.5 0.64 0.45 thickness for the inner h/d 0.19 0.19 0.19 p/d1.27 1.27 1.0

The following points are considered for the analysis model.

(a) It is difficult to build a detailed head impact model on theassumption of actual objects. The head is formed into a spherical headmodel. The car body is formed into a simple model comprising a hoodstructure and a rigid object surface.

(b) The rigid object surface simulates rigid objects including an enginethat are difficult to be modeled in the engine room. The rigid objectsurface is curved parallel to the outer and provides clearance L in theimpact direction. Car parts such as a fender, a window shield, and asuspension are not modeled.

(c) The hood model is intended for a normal sedan and comprises theinner of a 5000-series aluminum material and the outer of a 6000-seriesaluminum material. The hood is provided as a simple model configured tobe an elastoplastic, double corrugated structure having doublecurvatures, i.e., the curvature of 3100 mm in the longer direction ofthe hood and the curvature of 4300 mm in the width direction.

(d) The bonding section between the outer and the inner is not modeled.Thickness c of the bonding section is modeled to allow a gap. Threeblack triangles in FIGS. 18 and 19 work as supporting sections. Theother positions are not restricted. The hood structure impacts on a headto deform greatly. An impact section impacts on the rigid objectsurface.

(e) The head models follow child and adult head models indicated in theEEVC/WG10 requirements. The heads are simply modeled as rigid sphereswhose outside peripheries are covered with a skin having an eventhickness. We used an elastic material for the skin and determined itselastic modulus so that an acceleration response satisfies a specifiedrange during a drop test requested by EEVC/WG10. Table 2 lists thephysical values.

(f) We determined the height, the length, the plate thickness, etc. ofthe corrugated inner after detailed examinations from the viewpoint ofdecreasing the HIC value. We first paid attention to a child head thatgenerates a small kinetic energy and does not require severe impactconditions. After various examinations, we determined the values in thetable for dimensions of the corrugated hood structure.

The following similarity rule takes effect in an impact problem. Let usassume that two similar structures are subject to the same impact speedand are characterized by the same physical values such as an elasticmodulus, a yield stress, a gravity, and the like. Then, an accelerationresponse occurring at a specific position of the structures is inverselyproportional to a scale ratio. The larger structure produces a smalleracceleration.

When the child analysis model is expanded to the adult analysis model,both are subject to the same impact speed while impact angles differ.Assuming that the similarity rule is applicable, let us multiply thecorrugated hood structure geometry by a ratio of outside head diameters(a scale ratio of 1.27 times) to determine the corrugated hood structurefor the adult head impact model. Then, the head acceleration shouldreduce to 0.79 times to decrease the HIC value. However, the sameclearance is used for both. The similarity rule cannot be applied as is.On the contrary, the HIC value tends to increase. Here, we conductedseveral numerical analyses for the remaining parameters to determine ashape for the adult head impact.

First, the corrugation height is multiplied by the scale ratio. Next,the corrugation length and the outer plate thickness are set to the sameas the dimensions for the child head impact. The inner plate thicknessis increased slightly. Table 3 lists dimensions for the adult headimpact. The same corrugation length is used for the following reason.When the hood is designed, the child head impact causes a problem aheadof WAD1500, and the adult head impact causes a problem behind WAD1500.If a constant corrugation length is ensured in the boundary area ofWAD1500, the formal discontinuity can be avoided. This is favorable tothe design.

(g) The beam-type hood structure is based on the corrugated hoodstructure and employs a beam shape only for the inner structure. Thecross-sectional shape of the frame is approximately configured to betrapezoidal with reference to existing design examples.

(1) EXAMPLE 1 Comparison between the Beam-Type Hood Structure and theCorrugated Hood Structure

FIG. 22 shows analysis results of head impacts on the beam-type hoodstructure and the corrugated hood structure. The adult head model isused. There is 84 mm clearance L between the outer and the rigid objectsurface along the impact direction. An impact position is set to thecenter of the hood as shown in FIGS. 18 and 19. From FIG. 22, we canfind the following. The beam-type hood structure yields the HIC value of2059. The corrugated hood structure greatly decreases the secondacceleration wave. As a result, the HIC value greatly decreases to 940.The sine shape of the corrugated inner is suitable for absorbing animpact during the head impact. The head impact causes a backlashvibration between the outer and the inner to disturb the headacceleration waveform. This decreases the peak value and greatlydecreases the HIC value.

(2) EXAMPLE 2 Bonding the Corrugated Inner to the Outer

As analysis models, the outer and the inner are modeled to leave a 4 mmgap at the bonding section. Actually, the bonding section needs to beminimized to provide an optimal tension rigidity for the hood. Afterexaminations, we confirmed the following. In order not to hinder abacklash vibration, the contact cross-sectional shape preferably has arelatively limited area. As shown in FIG. 21, it is preferable toarrange the bonding sections on tops of the corrugated inner in across-stitched or distributed manner using very soft, spongy adhesive.We also confirmed the following tendency. When the cross sectional areaof the bonding section or the adhesive rigidity increases, the outer andthe inner are integrated to be vibrated easily, thus eliminating abacklash vibration. As a result, the second acceleration wave increasesto increase the HIC value.

(3) EXAMPLE 3 Preferred Ranges of Corrugation Length p and CorrugationHeight h

We investigated an effect of the corrugation length and the corrugationheight of the corrugated inner on HIC values. The outer plate thicknessis set to 1 mm. The inner plate thickness is set to 0.8 mm. With respectto analysis results of the child head impact, FIG. 23 shows an effect ofthe corrugation length on HIC values. FIG. 24 shows an effect of thecorrugation height on HIC values. According to FIG. 23, we can formulatea preferable range of corrugation length p effective for decreasing theHIC value as follows using outside head diameter d.0.7<p/d<1.7

According to FIG. 24, we can formulate a preferable range of corrugationheight h as follows also using outside head diameter d.0.15<h/d<0.4

If the corrugation length p is smaller than this range, the bendingrigidity of the corrugated inner increases along the longer direction ofthe hood. On the contrary, the bending rigidity decreases along thewidth direction of the hood. This decreases the inner rigidity in caseof the head impact and increases the HIC value. If the corrugationlength p is greater than this range, the bending rigidity increasesalong the width direction of the hood. On the contrary, the bendingrigidity decreases along the longer direction of the hood. Thisdecreases the inner rigidity in case of the head impact and increasesthe HIC value. In this manner, there is a preferable range forcorrugation length p. The range preferably covers approximate valueswith reference to the outside head diameter. This is because of thefollowing fact. In case of the head impact, the structure usesapproximately one corrugation to support the head and deforms to softlycatch the head. As a result, the HIC value can be decreased.

If the corrugation height h is smaller than the above-mentioned range,the corrugated inner is subject to an insufficient local bendingrigidity. It is impossible to absorb a head impact energy. The headimpacts on the rigid object surface to increase the HIC value. If thecorrugation height h is greater than the range, the corrugated inner issubject to an excess local bending rigidity. Since the hood rigidity istoo high, the HIC value increases. In this manner, there is also apreferable range for corrugation height h. It is preferable to design across-sectional shape of the corrugated inner based on theabove-mentioned preferable ranges.

If the clearance is constant, the HIC value for the adult head impactincreases in comparison with the HIC value for the child head impact. Inthis case, however, the preferable range of corrugation heights isconsidered to be almost the same as that for the child head impact.

(4) EXAMPLE 4 Effect of Head Impact Positions

FIG. 25 shows head impact positions for the child head impact under thecondition of 75 mm clearance L between the outer and the rigid objectsurface. Table 4 lists HIC values for the corresponding impactpositions. From this table, it can be understood that the HIC values areapproximately constant even if the head impact positions vary. Theuniformity of HIC values for impact positions is a very useful featureof the corrugated hood structure.

TABLE 4 EFFECTS DUE TO IMPACT POINT FOR HIC_VALUE CHILD_HEAD,CLEARANCE_L = 75 MM POINT HIC 1 820 2 947 3 757 4 903 5 820 6 882 7 7998 926 9 890 10 1106 11 978 12 1105 13 892 14 984 15 1011 16 964 17 96818 985 19 1013 20 1043 21 1016 22 1036

(5) Relationship between an HIC Value and Clearance L

FIG. 26 shows the relationship between an HIC value and clearance L. Weexamined the beam-type hood structure, the corrugated hood structure,and a corrugated hood structure with the inner center reinforced byincreasing the plate thickness with respect to the child head impact andthe adult head impact.

From the analysis results, we can conclude the following.

(a) The corrugated hood structure greatly decreases HIC values comparedto the beam-type hood structure.

(b) It can be understood that the corrugated hood structure slightlydecreases HIC values to decrease clearance L by reinforcing the platethickness at the inner center. It is possible to decrease clearance Lonly by locally increasing the inner weight. This is very useful for thedesign.

(c) The following shows a regression equation for experiment values incase of the adult head impact on the steel beam-type hood structure(MATSUI and ISHIKAWA, Crush Characteristics and HIC Values in FrontWindshield Areas in Pedestrian Head Impacts, JARI Research Journal,April 2000, Vol.22 No. 4). FIG. 26 shows a result.Y _(HIC)=5.4×10⁶ X ^(−1.95)

where Y_(HIC) is an HIC value and X is a dynamical deformation amount atthe head.

Clearance L between the outer and the rigid object surface is unknown tothe regression equation for experiment values. The equation usesdynamical deformation amounts along the head impact direction asarguments. It is impossible to make a direct comparison with theanalysis results by plotting clearance L between the outer and the rigidobject surface on the abscissa. However, both tendencies approximatelycorrespond with each other. The minimum clearance of 82.2 mm satisfiesthe HIC value 1000 obtained from the experiment result. This isapproximately the same value as 83 mm obtained from the analysis result.At first glance, the corrugated hood structure seems to provide nomerits. According to the analysis, however, the corrugated hoodstructure remarkably decreases HIC values compared to the beam-type hoodstructure. The HIC values obtained here for the simple model areexcessively calculated for the purpose of simplification. It isconsidered that experiment values will show a much smaller value as theminimum value of clearance L for the corrugated hood structure. Here, wemade no experiment on the corrugated inner structure for economicalreasons. We consider that this point will be confirmed in the future.

(6) EXAMPLE 6 Decreasing HIC Values at the Hood Periphery

The head impact resistance for pedestrian protection is subject toeffects of highly rigid positions such as a fender, the bottom of awindow field frame, and the like at the hood periphery. It is known thata high HIC value results if the head impacts on these positions.According to many conventional design examples, the bead provided at thehood periphery has the cross-sectional shape approximate to a trapezoid.This cross-sectional shape causes high HIC values. As a countermeasureto this, it is preferable to provide the inner periphery with corrugatedbeads whose cross-sectional shape is or approximates to a sine wave.These beads can decrease HIC values at the above-mentioned positions.

FIG. 27 shows an example. The corrugation length, the corrugationheight, and the cross-sectional shape at these peripheries aredetermined in consideration for the bending rigidity, the torsionalrigidity, and the like. The corrugation length and the corrugationheight need not be uniform on the entire surface of the hood. The mostpreferable corrugation length and corrugation height should bedetermined in consideration for the design requirements at respectivehood positions. The hood periphery is especially subject to effects ofhighly rigid positions such as the fender, the bottom of the windowfield frame, and the like. For example, halving the corrugation lengthensures a clearance between the outer and the inner to decrease HICvalues.

(7) EXAMPLE 7 Corrugated Hood Structure Comprising a Steel Outer and anAluminum Alloy Spline-Type Inner

The following description uses the spline-type inner and presents anexample of the corrugated hood structure comprising the steel outer andthe aluminum alloy inner. FIG. 28 shows the inner shape. FIG. 29 showsthe positional relationship between the inner and the rigid objectsurface, and head impact positions.

This model uses several rigid object surfaces parallel to the outer tosimply model the top surfaces of rigid objects such as an engine, abattery, and the like. For simplicity, there is provided a 70 mm uniformclearance between the outer and the rigid object surface in the verticaldirection. The outer is made of an SS330-equivalent steel plate 0.7 mmthick. The inner is made of an aluminum 5000-series alloy 1.2 mm thick.Impact positions for the adult head are allotted on the WAD1500 line(impact positions 1 to 4). Impact positions for the child head areallotted on the WAD1500 line (impact positions 1 to 4) and on theWAD1100 line (impact positions 5 to 8) FIG. 30 shows a head accelerationwaveform for the child head impact at impact position 1. FIG. 31 shows ahead acceleration waveform for the adult head impact at impact position1. Table 5 lists analysis results.

The analysis results have made clear the following facts.

(a) Except impact position 4, the condition of HIC value 1000 is almostsatisfied for the adult and the child, yielding a good result.

(b) In case of the child head, the first acceleration wave showsapproximately 200 G, producing an ideal head acceleration waveform. Theouter absorbs almost all the kinetic energy. The second accelerationwave does not affect computation of HIC values. This is confirmed by thefact that time ranges t1 and t2 for computing HIC values in FIG. 30 areonly applicable to the first acceleration wave.

(c) In case of the adult head, the HIC value of 1000 is approximatelysatisfied except impact position 4. The values for impact positions 1and 2 slightly exceed the HIC value of 1000. This degree of fluctuationscan be easily solved by examining the inner shape, the plate thickness,and the like in detail.

(d) The HIC values for the corresponding hood positions areappropriately controlled. We confirmed an effect of designing thespline-type inner in consideration for an impact on rigid objectscomplexly arranged in the engine room.

The adult head is subject to a head impact energy 1.92 times greaterthan the child head impact. When the above-mentioned similarity rule isapplied, the steel outer causing the first acceleration wave of 200 Gwill have the plate thickness of 0.9 mm that is 1.27 times as large asthe thickness of 0.7 mm. However, this plate thickness causes a valueexceeding the HIC value of 1000 for the child head impact and isinappropriate for the child head impact. For this reason, the maximumplate thickness of the steel outer is 0.7 mm in consideration for boththe adult and the child. In this case, the first acceleration wave forthe adult head ranges from 120 to 150 G according to Table 5. The outerinsufficiently absorbs the impact energy. The second acceleration waveneeds to absorb the remaining kinetic energy. According to the priornumerical analysis, the plate thickness needed for the aluminum alloyinner is found to be 1.2 mm. The above-mentioned analysis model usesthis value.

The analysis result here shows that the HIC value of 1000 is almostsatisfied except impact position 4.

If the outer is made of an aluminum alloy, the outer's mass must be thesame as that of the steel plate. In this case, the outer plate thicknessbecomes 2.1 mm, increasing costs. Accordingly, the use of the aluminumouter provides no merits.

If the inner is made of steel, the steel plate thickness is found on thecondition that the inner provides the same bending rigidity as that ofthe aluminum alloy plate 1.2 mm thick. Assuming the same bendingrigidity as mentioned above, there is a plate thickness ratio of 1.44between the aluminum alloy and the steel plate. The steel platethickness is found to be 0.83 mm by dividing 1.2 mm by 1.44. In thiscase, the steel inner weighs approximately twice the aluminum alloyinner. This is disadvantageous to weight saving.

As a result, it has been made clear that the corrugated hood structurecomprising the steel outer and the aluminum alloy inner provideslight-weight and low-cost hoods for large sedans and the like needed tosatisfy both child and adult head impacts.

Unlike large sedans, medium-size or small-size cars can use anall-aluminum corrugated hood structure for their hoods if only the childhead impact needs to be considered and a sufficiently large clearancecan be ensured between the outer and the rigid object surface. If asufficiently large clearance cannot be ensured between the outer and therigid object surface, it is effective to use the above-mentionedcorrugated hood structure comprising the steel outer and the aluminumalloy inner.

The cone-type hood structure comprising the steel outer and the aluminuminner provides a certain effect of decreasing HIC values, not socomparable to the corrugated inner.

TABLE 5 On line WAD 1500 On line WAD1100 Head impact position 1 2 3 4 56 7 8 Adult HIC value 1053 1061 923 1435 — — — — head First acceleration152 140 120 120 — — — — wave (G) Second acceleration 120 115 112 150 — —— — wave (G) Child HIC value 970 908 907 1215 989 1056 956 770 headFirst acceleration 200 189 180 181 212  183 200 140 wave (G) Secondacceleration * * * 133 165  100 117  80 wave (G) An asterisk * indicatesthat the second acceleration wave does not contribute to computation ofHIC values.

(8) EXAMPLE 8 Cone-Type Hood Structure Comprising a Steel Outer and anAluminum Alloy Cone-Type Inner

Example 8 describes the cone-type hood structure comprising the steelouter and the aluminum alloy inner according to claim 12. That is tosay, we analyzed this cone-type inner in a manner similar to that forexample 7. We examined head impact positions in two case, i.e., a conevertex at the hood center and a middle between cone vertexes. FIG. 32shows an analysis result for the child head impact. FIG. 33 shows ananalysis result for the adult head impact. According to these figures,it is clear that an HIC value between the cone vertexes is larger thanan HIC value at the cone vertex. This is because of the followingreason. When the head impacts on a middle between the cone vertexes, thecone deformation greatly decreases absorption of the impact energy. Thehead impacts on the outer, and then straightly on the rigid object. Itcan also be seen that an HIC value for the adult head impact is largerthan an HIC value for the child head impact. This tendency is the sameas that for the corrugated hood structure. Further, we confirmed thatchanging the outer material from the aluminum alloy to the steel greatlydecreases HIC values. As a result, it has been confirmed that, like thecorrugated hood structure, the cone-type hood structure using the steelouter effectively decreases HIC values.

INDUSTRIAL APPLICABILITY

The present invention relates to a panel structure used for car bodyhoods.

1. A car body hood panel structure as a closed sectional structurecomprising a combination of: an outer panel; an inner panel, wherein aplurality of corrugated beads is provided parallel to each other on amajor part of a surface of said inner panel such that a cross-sectionalshape of said inner panel is corrugated; and an adhesive joining thecorrugations of the inner panel with the outer panel, wherein the crosssectional corrugated shape of the inner panel satisfies the relationship91 mm<p<221 mm, where p is a length of an entirety of each of thecorrugations.
 2. The car body hood panel structure according to claim 1,wherein said corrugated shape follows a sine curve or annth-power-raised sine curve.
 3. The car body hood panel structureaccording to claim 1, wherein said plurality of corrugated beads isprovided in at least one arrangement selected from those which areparallel or slantwise against a longer direction of said panelstructure, concentric approximately around the center of said panelstructure, and doubly corrugated.
 4. The car body hood panel structureaccording to claim 1, wherein one of said outer panel and said innerpanel is aluminum alloy or steel.
 5. The car body hood panel structureaccording to claim 1, wherein the cross sectional corrugated shape ofsaid inner panel satisfies the relationship 19.5 mm<h<52 mm, where h isa corrugation height.
 6. The car body hood panel structure according toclaim 1, wherein a reinforce panel is provided to part of said innerpanel.
 7. The car body hood panel structure according to claim 1,wherein said adhesive is a resin, whereby said inner panel and saidouter panel are softly joined at one of said corrugated beads of saidinner panel.
 8. The car body hood panel structure according to claim 1,wherein said inner panel is joined to said outer panel at saidcorrugated beads by means of soft joining sections which are arranged ina cross-stitched manner.
 9. The car body hood panel structure accordingto claim 1, wherein said corrugated shape is defined by a splinefunction.
 10. The car body hood panel structure according to claim 1,wherein said outer panel is steel and said inner panel is an aluminumalloy corrugated inner panel.